There are a lot of burglar alarms on the market, but those burglar alarms mostly depend on minute vibrations to detect a door being opened, or on vibration switches on the doors and windows to detect whether they are being opened or broken. Meanwhile, there are also various devices which can detect movements from burglars and provide protection on line by means by ultrasonic detectors, microwave detectors or infrared detectors. These frequently used devices using ultrasonic detectors, microwave detectors or infrared detectors are all designed for detecting moving objects, and so, false alarms may be caused by cats, dogs, flying insects or the movements of curtains. As for vibration switches, they are easily triggered by nonburglar interruption; therefore, they are apt to cause trouble when being used. Devices using ultrasonic detectors, microwave detectors or infrared detectors etc., are often too sensitive in operation and will also sometimes malfunction if they are affected by minute movements from their surroundings. On the other hand, if the devices are under the required sensitivity, they cannot be considered effective. Accordingly, the appropriate sensitivity of burglar alarm devices is truly an important problem.
In protecting one locality or more than one localities, average burglar alarms might be adjusted to the proper distance and equipped with an interruption demonstrator; however, false alarms could still occur. This new invention has installed two identical or different detectors, equipped with a multi-phase detection instrument. The above detectors can detect in one or different localities so that when two detectors detect the movement within a preset period, then the burglar alarm shall be triggered. If the two detectors have detected the signal at different moments, the controlling circuit will automatically reject the triggering signal and reset the detectors. The chance of causing false alarms will be avoided and so, the function of protection provided by the alarm will be greatly enhanced.